Die package with low electromagnetic interference interconnection

ABSTRACT

A die package having lead structures connecting to a die that provide for electromagnetic interference reductions. Mixed impedance leads connected to the die have a first lead with a first metal core, a dielectric layer surrounding the first metal core, and first outer metal layer connected to ground; and a second lead with a second metal core, and a second dielectric layer surrounding the second metal core, and a second outer metal layer connected to ground. Each lead reducing susceptibility to EMI and crosstalk.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to novel lead structures connecting to die thatprovide for electromagnetic interference reductions. Crosstalk betweenleads, as well as susceptibility to noise created by electromagneticemissions internal or external to the package, are reduced through theimplementation of the invention.

Further, the invention relates to novel multiple ground planes formed toconnect dielectric coated leads connecting to one or more dies.

2. Description of Related Art

Electromagnetic interference leading to reduced performance is anincreasingly common problem for packaged die, particularly for diehaving input/output (IO) operating at Gigahertz frequencies. Manyintegrated circuits generate undesirable amounts of EMI. Typically, thenoise generated by the integrated circuit originates from the die andits connections to the pins through the package. As the EMI is coupledto neighboring components and integrated circuits, it interferes withtheir individual performance which may, in turn, affect the overallperformance of a system. Because of the negative effects of EMI andbecause the level of acceptable radiated EMI is subject to strictregulatory limits, it is desirable to contain or suppress the EMIgenerated by an integrated circuit.

Solutions such as separation of leads or isolation with shields are notalways available or sufficient. Furthermore, EMI solutions at the ICpackage level are often ignored because the main concerns at that levelare signal integrity and functionality. It would be beneficial to havean EMI solution at the package level because it would help reduce theneed for “downstream” or add-on solutions.

SUMMARY OF THE INVENTION

Bearing in mind the problems and deficiencies of the prior art, it istherefore an object of the present invention to provide a compact diepackage and in particular a stacked die package and/or BGA package withtwo or more leads providing excellent signal integrity andfunctionality.

The above and other objects, which will be apparent to those skilled inthe art, are achieved in the present invention which is directed in afirst aspect to a die package for EMI attenuation, comprising a diehaving a plurality of connection pads; a die substrate supporting aplurality of connection elements; a first lead having a first metal corewith a first metal core diameter, a first dielectric layer surroundingsaid first metal core having a first dielectric thickness, and a firstouter metal layer surrounding said first dielectric layer, said firstouter metal layer attached to ground; and a second lead having a secondmetal core with a second metal core diameter, a second dielectric layersurrounding said second metal core having a second dielectric thickness,and a second outer metal layer surrounding said second dielectric layer,said second outer metal layer attached to ground; such that said firstand second leads reduce susceptibility to EMI and crosstalk betweenfirst and second leads.

Further, the present invention is directed in a second aspect to a diepackage, comprising a die having a plurality of connection pads; a diesubstrate supporting a plurality of connection elements; a first leadhaving a first metal core with a first metal core diameter, a firstdielectric layer surrounding said first metal core having a firstdielectric thickness, and a first outer metal layer surrounding saidfirst dielectric layer, with a first ground plane being attached to thefirst outer metal layer; and a second lead having a second metal corewith a second metal core diameter, a second dielectric layer surroundingsaid second metal core having a second dielectric thickness, and asecond outer metal layer surrounding said second dielectric layer, witha second ground plane being attached to the second outer metal layer;such that said first and second leads reduce susceptibility to EMI andcrosstalk between the first and second leads. The first lead may extendfrom a first die to one of the plurality of connection elements on thedie substrate and/or the second lead may extend from a second die to oneof the plurality of connection elements on the dies substrate. Thesecond ground plane may or may not overlay the first ground plane. Inthe case of an overlay, an intervening layer maintaining electricalisolation may be arranged between the first and second ground planes.

In an additional aspect, the die package according to the invention maybe a stacked die package with a first and a second die, each of saiddies having a plurality of connection pads; the first lead extendingfrom one of said plurality of connection pads of said first die to oneof said plurality of connection elements on said die substrate or to oneof said plurality of connection pads of said second die, and the secondlead extending from one of said plurality of connection pads of saidsecond die to one of said plurality of connection elements on said diesubstrate or to one of said plurality of connection pads of said firstdie.

The dependent claims are directed to advantageous embodiments of the diepackages according to the invention, and the respective featuresdisclosed therein may be added separately or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is an illustration of a fine pitch, low crosstalk die packagewith dielectric coated leads with outer ground connected metallization;

FIG. 2 illustrates low crosstalk overlapping dielectric coated leadswith outer ground connected metallization;

FIG. 3 illustrates low crosstalk leads used in stacked die packages;

FIG. 4 illustrates low crosstalk leads used in die to die or package topackage embodiments;

FIG. 5 is a block diagram illustrating method steps for manufacture ofdielectric coated leads with outer ground connected metallization;

FIG. 6 illustrates a subtractive method for manufacture of dielectriccoated leads with outer ground connected metallization;

FIG. 7 illustrates a BGA package having dielectric coated leads withouter ground connected metallization;

FIG. 8 illustrates a portion of leadframe package having dielectriccoated leads with outer ground connected metallization;

FIGS. 9A and 9B illustrate S-parameter measurements of frequency basedcrosstalk levels;

FIGS. 10A-D illustrate EM fields associated with single and differentialleads with dielectric coating and outer ground connected metal layer,respectively;

FIGS. 11a and 11b illustrate die packages in accordance with theinvention with leads coated with a dielectric and metal connected toseparate ground planes that may or may not overlap;

FIG. 12 illustrates a die package in accordance with the invention withtwo ground planes; and

FIG. 13 illustrates a further example embodiment with two ground planesrespectively forming an RF ground shield and a DC power shield.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1-13 of the drawings in whichlike numerals refer to like features of the invention.

Leads having electromagnetic shielding and one or more intermediatedielectric layers between a metal core and a ground connectableconductive outer layer can be used to improve package electricalperformance. This is depicted in FIG. 1, which illustrates package 150that includes a die 152 attached to a substrate 154 with leads 156 ofdiffering length. As is apparent, connection pads 158 on substrate 154are usually at a larger spacing than at the chip side because of processconsiderations. Die pad spacing is commonly defined by the pitchachievable by the wire bonding machinery. On the substrate side, pitchis defined by the lithographic repeatability for printed circuit board(PCB) type processes and solder, pin, or interconnect element placementaccuracy. In practice, wires are spaced more closely at the chip than onthe package. This means that as die sizes are reduced, more undesirableelectromagnetic field coupling (crosstalk) occurs on the wires,especially in the vicinity of the die. In addition to reducingin-package electromagnetic interference (EMI), leads constructed asdescribed herein have reduced susceptibility to external (to thepackage) EMI, and will have substantially reduced electromagneticemissions as well.

As seen in FIG. 2, a semiconductor die packaging system 100 can beformed to have leads 110, 112, and 114 that have low electromagneticemissions and crosstalk due to lead construction. The die 120, mountedon substrate 102, includes multiple connection pads 122 for signal,power, or other functionality required by the die 120. Substrate 102 mayinclude conductive pads 104 that provide an electrically conductive pathout of the package directly or through conductive leadframes, filledvias, conductive traces, second level interconnections, or like. Leads110, 112, and 114 connect to conductive pads 104, and as illustrated,may have substantially different lengths. As is seen in FIG. 2, leadsare narrowly spaced, and are capable of crossing over or under oneanother (for example, leads 110 and 112 are depicted as crossing over),providing many opportunities for undesirable electromagnetic coupling.

In the illustrated embodiment, leads 110, 112, and 114 have an innercore and an outer metal layer. For example leads 110, 112, and 114 canhave a metal core of a defined diameter along its length, the metal corebeing sequentially coated with a dielectric layer and a conductive metallayer. As compared to a bare lead of the same size without additionaldielectric and metal coatings, leads 110, 112, and 114 emit lessradiation, are less susceptible to external (to the package) EMI, andless prone to crosstalk. In certain embodiments, due to the superiorelectrical characteristics of lead construction as disclosed, leadshaving substantially different lengths but the same core diameter canhave substantially the same noise reduction as compared to a bare wire.The measured noise reduction has been shown to be greater than 5 dB toas much as 30 dB over performance compared to a bare lead withoutdielectric and surrounding metal layer(s). In certain embodiments,resistance to EMI is effective over a range of lead lengths, with twoleads capable of having the same cross sectional structure andimpedance, but one lead being ten (10) times the length of the other,while still having the same EMI characteristics.

Electromagnetic field coupling leading to unwanted crosstalk occurs notjust on leads that are side by side, but can also occur on leads thatare near each other in stacked configurations. This is realized in astacked die configuration as depicted in FIG. 3, which illustratesstacked die package 160 having dies 162 a-d with exemplary leads 164 a-dand 166 a-d that would create unacceptable crosstalk from leads side byside, above, and below if bare wires were used, rather than leads coatedwith a dielectric layer and a conductive metal layer as describedherein. Similarly, FIG. 4 illustrates die stacks 170 and 172 having dieto die lead connections 174, and die to substrate connections 176. Theremay also be direct die to die connections 178 in separately mountedpackaging systems 180, 182 with reduced crosstalk.

Dielectric coated leads used in semiconductor die packages can be formedto have varying dielectric thickness. Both the core diameter and thedielectric thickness may be varied. In certain embodiments, compositionof the deposited dielectric may also be varied. This allows, forexample, a high performance dielectric having superior vapor barrier,oxygen degradation resistance, or the like, to be thinly deposited overa thick layer of a low cost dielectric material. In another aspect ofthe illustrated embodiment, leads 110, 112, and 114 (refer: FIGS. 2 and3) have varying dielectric thickness over an inner core and an outermetal layer, which provide for distinctly different impedances. Forexample, leads 110 may have a metal core of a defined diameter along itslength, the metal core being sequentially coated with a thin dielectriclayer and a conductive metal layer. Such leads 110 are suitable fortransfer of power because the consequent low impedance and lowcapacitance reduces power sag. Alternatively, leads 112 have a muchthicker dielectric layer suitable for transmission of signal data, whileleads 114 have a dielectric layer of intermediate thickness. In certainembodiments, due to the superior electrical characteristics of leadconstruction as disclosed, it is possible for leads having substantiallydifferent lengths but the same core diameter to have substantially thesame impedance, within 10% of target impedance, despite having lengthsthat vary 50% or greater. For example, lead 116 may have about the sameimpedance as lead 110, despite being twice as long. In certainembodiments, lead differences may be even greater, with two leads havingthe same cross sectional structure and impedance, but one lead being ten(10) times the length of the other.

Generally, thin dielectric layers will provide low impedance which isbeneficial for power line applications; thick dielectric layers aregenerally beneficial for signal integrity; and outer metal layers on theleads may be advantageously connected to same ground. A combination ofcore diameters and dielectric thicknesses is possible and a series ofsuch steps may be performed to achieve leads having differingimpedances. In certain embodiments it may be desirable to have largecores on power lines to increase power handling capacity, reduce powerline temperatures, and/or further reduce any inductance on power supplyand ground lines that would exacerbate ground bounce or power sag.

Dielectric layers of intermediate thickness are also useful, since manypackages could benefit from having leads of three (3) or more differentdielectric thicknesses. A lead having an intermediate dielectricthickness could be used to connect a source and load of substantiallydifferent impedance to maximize power transfer. For example, a 10 ohmsource can be coupled to a 40 ohm load with a 20 ohm lead. Also, sincecost of dielectric can be high, critical signal pathways may beinterconnected using thick dielectric, while less critical status orreset leads, or the like, are coated with a dielectric layer having athickness greater than the power leads, but less than (intermediate) tothe critical signal leads. Advantageously, this can reduce dielectricdeposition material cost and time.

The precise thickness of the dielectric coating may be chosen, incombination with the wirebond diameter, to achieve a particular desiredimpedance value for each lead.

$\begin{matrix}{Z_{0} = {\sqrt{\frac{L}{C}} = {\frac{138}{\sqrt{ɛ_{r}}} \cdot {\log\left( \frac{b}{a} \right)}}}} & (1)\end{matrix}$

The characteristic impedance of a coax line is given in Eq. (1), where Lis the inductance per unit length, C is the capacitance per unit length,a is the diameter of the bond wire, b is the outside diameter of thedielectric and ∈_(r) is relative permittivity of the coaxial dielectric.

As illustrated in FIG. 5, in one embodiment manufacture of dielectriccoated leads with outer ground connected metallization with or withoutone or more ground planes can proceed using the following stepsillustrated in block diagram 200. In a first step 202, connection padsare cleaned on the die and the substrate. Next, a wire bonder is used toconnect the die to the connection pads 204. Optionally, a seconddiameter wire can be attached 206 (e.g., a larger diameter wire suitablefor power connections), or areas of the die can be masked or otherwiseprotected to allow for selective deposition, step 208. One or morelayers of dielectric of the same or different composition may bedeposited (step 210), followed by selective laser or thermal ablation,or chemical removal of portions of the dielectric to allow access toground connections (step 212) covered in the dielectric deposition step210. This step is optional, since in some embodiments, the need for aground via may be eliminated. This is particularly true for dieoperating at higher frequencies, since a virtual RF ground may beestablished through capacitive coupling and since frequency dependenceon thickness value (function of ∈_(r)) allows for ground establishmentthrough capacitive coupling. Metallization follows (step 214), coveringthe dielectric with a metal layer that forms the outermost metallizedlayer of the leads, and also connecting the leads to ground. The entireprocess can be repeated multiple times (step 216), useful for thoseembodiments using selective deposition techniques, and particularly forthose embodiments supporting multiple die or complex and variedimpedance leads. In the final step (step 218), for non-cavity packages,an overmold can be used to encapsulate leads. The encapsulated leads maybe used in high frequency device packages described in U.S. Pat. No.6,770,822 and in U.S. Pat. No. 8,839,508.

In certain embodiments, modifications and additions to the describedprocess are possible. For example, providing conformal coatings ofdielectric can be accomplished through a variety of methods usingchemical (electrophoretic), mechanical (surface tension), catalyticprimer, electromagnetic (UV, IR), electron beam, or other suitabletechniques. Electrophoretic polymers are particularly advantageousbecause they can rely on self-limiting reactions that can depositprecise thicknesses readily by adjusting process parameters and orsimple additive, concentration, chemical, thermal, or timing changes toan electrophoretic coating solution.

In other embodiments, dielectric precoated bondwires can be used to formleads. While commercially available coated wires typically are thinnerin dielectric thickness than is necessary to create, for example, 50 ohmleads, the foregoing discussed dielectric deposition steps can be usedto increase dielectric thickness to set the desired impedance. Use ofthese pre-coated wires can simplify other process steps necessary tocreate coaxial leads, and can allow for thinner layers of needed vapordeposited dielectrics and faster processing times to create ground vias.Pre-coated bondwires may be used to prevent shorting for narrowly spacedor crossing leads. In certain embodiments the pre-coated bondwire mayhave a dielectric made from a photosensitive material to allow forselective patterning techniques.

In other embodiments, the dielectric Parylene™ can be used. Parylene™ isthe trade name for a variety of chemical vapor depositedpoly(p-xylylene) polymers used as moisture and dielectric barriers.Parylene™ can be formed in a growth limited condensation reaction usinga modified Parylene™ deposition system where the die, substrate, andleads are aligned to a photoplate which allows EM radiation (IR, UV, orother) to strike in a precise manner causing selective growth rate ofdielectric. Advantageously, this can minimize or eliminate the need forprocesses to create contact vias, bulk removal of Parylene™, etc.

Parylene™ and other dielectrics are known to suffer from degradation dueto oxygen scission in the presence of oxygen, water vapor, and heat.Damage can be limited by metal layers that form excellent oxygen vaporbarriers, with thin layers of 3-5 micron thickness capable of formingtrue hermetic interfaces. Alternatively, if metal has been selectivelyremoved, or not deposited in certain areas due to electrical, thermal,or manufacturing requirements, a wide range of polymer based vaporoxygen barriers can be used, with polyvinyl alcohol (PVA) being onewidely used polymer. These polymers can be glob topped, screen printed,stenciled, gantry dispensed, sprayed onto Parylene™ surface that will beexposed to the oxygen or water vapor environment. Advantageously, use ofvapor barrier polymers can be a part of a cost reduction strategy, sincethicker layers of high cost Parylene™ or other oxygen sensitive mightotherwise be required.

As will be appreciated, all of the described method steps can benefitfrom various selective deposition techniques. Selective deposition canbe by physical masking, directed polymer deposition, photoresistmethods, or any other suitable method for ensuring differentialdeposition thickness on the metal core, dielectric layer, or otheroutermost layer at time of deposition. While selective deposition allowsfor additive methods to build leads, it also allows for subtractivetechniques in which dielectric or metal is removed to form interconnectsof differing impedances. For example, a package populated by one or moredie can be wire-bonded as appropriate for interconnect of all packageand device pads. As seen with respect to FIG. 6, which illustrate stepsand structures for manufacture of a die package, the dielectric coating300 can be deposited to a predetermined thickness over a wirebond metalconductor 302 (step A), where the predetermined thickness of thedielectric is necessary for the secondary interconnect impedance. Thesecondary impedance wirebond dielectrics can be removed for example byan etch step (step B), followed by a second coating 304 deposition (stepC) followed by metallization 306 of both interconnects (step D). Thissubtractive process will create wirebonds of two distinct impedances.

In an embodiment illustrated with respect to FIG. 7, a ball grid array(BGA) package 410 that includes dielectric and metal coated leads 412,414 having multiple selected impedances is described. A BGA is asurface-mount packaging widely used for integrated circuits, and cangenerally provide more interconnection pins than dual in-line,leadframe, or other flat package since the entire bottom surface of theBGA can be used for connection pads. In many types of BGA packages, adie 416 is attached to a substrate 418 having Tillable vias 420connected to connection pads. Wirebonds 412, 414 may be used to connectthe top side die 416 to the pads/vias 420, consequently providingelectrical connections from a top side of the substrate 418 to thebottom. In a BGA package, balls of solder 422 are attached to the bottomof the package and held in place with a tacky flux until soldering to aprinted circuit board or other substrate. As described herein, thewirebonds of conventional BGA packages can be replaced with improvedleads having a dielectric layer and an outer ground connectable metallayer. The leads can have varying dielectric thickness over an innercore and an outer metal layer, as well as being selectively optimized tohave specific impedances, which can be selected to be different orwell-matched based in part on dielectric layer thickness. As seen in theFIG. 7, both long leads 412 and short leads 414 are supported.

In more detail, assembly of an improved BGA package can require face upattachment of a die to a substrate supporting a connection pad formedadjacent and around a via in the substrate. This assembly is wirebondedas appropriate for each required interconnect, with a wirebond formedbetween a connection pad on the substrate and a connection pad on thedie. Low frequency and power inputs are connected to the low frequencysignal leads, while high-frequency inputs and outputs are connected tothe high frequency signal leads. In some embodiments, the low frequencyand power inputs can have a thickness that differs from high frequencysignal leads. The assembly is then subjected to the coating of anyessentially conformal dielectric material. Because of its low cost, easeof vacuum deposition, and superior performance characteristics,Parylene™ is preferably used. A small part of the dielectric layer nearthe leadframe attachment point can be selectively removed by etch,thermal degradation, or laser ablation, in order to form electricalconnection to a ground contact point or ground shield layer. Similarly,a small portion of the dielectric layer is removed near the dieconnection pads to permit ground connections. Connection to ground inthe structure follows from application of a metallized layer over thetop of the dielectric layer, forming a ground shield. The thickness ofthe preferred metal layer should be chosen in consideration of skindepth and DC resistance issues, and should be composed primarily of anexcellent electrical conductor such as silver, copper, or gold. For mostapplications, a 1 micron coating thickness is adequate forfunctionality, but thicker coatings can help minimize cross-talk betweenleads. These coatings may be added in defined areas through acombination of lithography or other masking methods, and plating orother selective deposition methods. The package can be completed byplacement of an overmold or lid over the die, followed by dicing(singulation) and testing.

Alternatively, in an embodiment illustrated with respect to FIG. 8, lowcost leadframe based die package 440 including wire bonds extending fromthe die to a leadframe can be manufactured by forming a leadframe stripcontaining a two-dimensional array of individual package sites andoutside frame portion. Leadframe fabrication is conventional, and caninclude formation of separate leads through etching, stamping, orelectrodeposition. The leadframe strip can be placed in a moldincluding, but not limited to, an injection molding or transfer moldingapparatus. An appropriate dielectric material, preferably plastic suchas commercially available epoxy mold compound, is injected, pumped, orotherwise transferred into the mold to achieve a leadframe/mold materialcomposite structure. The properties of the mold material are importantfor their dielectric constant, loss tangent, and electrically dispersiveproperties as well as their temperature, moisture, and other mechanicalperformance attributes.

Each package site on the resulting composite leadframe strip is cleanedof mold release material and or mold-flash, and prepared for depositionof a metal finish over the exposed metal portions of the leadframe. Thismay be accomplished through plating techniques such as immersion orelectroplating, and the metals would be chosen for corrosion suppressionand ease of wirebonding. An example of such finishing is a thin layer ofnickel (for protection) followed by a layer of gold (added protectionand ability to wirebond). Each package site of the resultant moldedleadframe strip can then be populated with the required die, which areattached to the base with die attach material being chosen formechanical and thermal properties for a particular packagingapplication. The resultant assembly is then wirebonded as appropriatefor each required interconnect, with a wirebond formed between a lead onthe leadframe and a connection pad on the die. Low frequency and powerinputs are connected to the low frequency signal leads, whilehigh-frequency inputs and outputs are connected to the high frequencysignal leads. In some embodiments, the low frequency and power inputscan have a thickness that differs from high frequency signal leads.

Like the foregoing described BGA package 410, the populated leadframestrip is then subjected to the coating of any essentially conformaldielectric material including Parylene™. In the case of Parylene™, itmay be preferable to mask the bottom of the packages with tape, such asa vacuum-compatible polyimide with acrylic adhesive, or similar materialto prevent deposition onto the area of the leads that will eventuallyattached to the PCB. This will facilitate easier soldering at asubsequent step. A small part of the dielectric layer near the leadframeattachment point is selectively removed by etch, thermal degradation, orlaser ablation, in order to form electrical connection to a groundcontact point or ground shield layer. Similarly, a small portion of thedielectric layer is removed near the die connection pads to permitground connections. Connection to ground in the structure follows fromapplication of a metallized layer over the top of the dielectric layer,forming a ground shield. The thickness of the preferred metal layershould be chosen in consideration of skin depth and DC resistanceissues, and should be composed primarily of an excellent electricalconductor such as silver, copper, or gold. For most applications, a 1micron coating thickness is adequate for functionality, but thickercoatings can help minimize cross-talk between leads. These coatings maybe added in defined areas through a combination of lithography or othermasking methods, and plating or other selective deposition methods. Thepackage is completed by placement of an overmold or lid over the die,followed by dicing (singulation) and testing.

Example 1—Crosstalk Performance

FIG. 9A is a graph 500 depicting cross-talk comparison as a function offrequency of bare wirebond 502, 30 ohm coax 504, and 50 ohm coax 506.Both coaxial leads exhibit approximately 25 dB improvement incross-talk/isolation over the unshielded interconnect. In this regards,even a mismatched coaxial lead prepared according to the presentinvention is superior to an unshielded bare lead.

FIG. 9B is a graph 510 depicting comparison of bare bond 512, 514 and 50ohm coaxial leads 516, 518 behavior in time domain. Consistent with thefrequency results depicted in FIG. 9A, noise voltage is reduced as muchas 12-fold (cross-talk/isolation) 520 and settling time response isimproved 7-fold 522 (permitting increased bandwidth).

FIGS. 10A-D illustrate spatial amplitude plots of EM field amplitudesassociated with single and differential leads with and withoutdielectric coating and outer ground connected metal layer, respectively.FIG. 10A depicts an amplitude plot 600 of single ended bond wires 602.As shown, the EM field amplitude at a point along the y-axis of the bondwire is significant. FIG. 10B depicts an amplitude plot 610 of singleended micro coaxial lines 612. As is apparent, the coaxial leads havesubstantially reduced electromagnetic emissions as compared to bareleads.

This is of particularly utility for differential pairs, a techniquecommonly used with bare leads to improve noise immunity. Typically, apair of leads driven with signals that are at opposing polarities willbe subjected to roughly equal noise environments. When these two signalsare added together differentially, the common noise can be cancelledout. However, if noise environments are not equivalent, as can happenfor fine pitch placement of many pairs of leads, a neighboring noisesource can induce a larger signal on the nearest neighbor of thedifferential pair than on the farther neighbor. Shielded micro-coaxialpairs are thus much more noise immune because the noise is highlyattenuated before reaching the signal line. FIG. 10C depicts a spatialamplitude plot 620 of differential bond wires 622. FIG. 10D depicts aspatial amplitude plot 630 of differential micro-coaxial lines 632. Theplot presents almost complete shielding, that is, negligible emissionsof electromagnetic radiation.

As seen in FIGS. 11a and 11b a semiconductor die packaging system 1100can be formed to have multiple separated or overlapping ground planes.Leads 1110, 1112, and 1114 can be manufactured to have lowelectromagnetic emissions and crosstalk due to lead construction andconnection to a ground plane. The die 1120, mounted on die substrate1102, includes multiple connection pads 1122 for signal, power, or otherfunctionality required by the die 1120. The die substrate can includeconductive pads 1104 that provide an electrically conductive path out ofthe package, directly, or through conductive leadframes, filled vias,conductive traces, second level interconnections, or like. Leads 1110,1112, and 1114 connect to conductive pads 1104, and as illustrated, mayhave substantially different lengths.

In the illustrated embodiment, leads 1110 and 1112 have an inner coreand an outer metal layer connected to a first ground plane 1130. Incontrast, leads 1114, also have an inner core and an outer metal layeris connected to a second ground plane 1132 separate and distinct fromthe first ground plane 1130. Similarly, FIG. 11b illustrates a package1101 of equivalent design to package 11 a, with the exception thatground planes 1134 and 1136 physically overlap. The ground planes areelectrically distinct, however, since a dielectric coating 1138 (shownpartially removed) can be used to isolate the grounds 1134 and 1136 fromeach other. As will be understood, the leads 1110, 1112, and 1114 canhave a metal core of a defined diameter along its length, the metal corebeing sequentially coated with a dielectric layer and a conductive metallayer.

As compared to a bare lead of the same size without additionaldielectric and metal coatings, leads 1110, 1112, and 1114 emit lessradiation, are less susceptible to external (to the package) EMI, andless prone to crosstalk. In certain embodiments, due to the superiorelectrical characteristics of lead construction as disclosed, leadshaving substantially different lengths but the same core diameter canhave substantially the same noise reduction as compared to a bare wire.The measured noise reduction can be greater than 5 dB to as much as 30db over performance compared to a bare lead without dielectric andsurrounding metal layer. In certain embodiments, resistance to EMI iseffective over a range of lead lengths, with two leads capable of havingthe same cross sectional structure and impedance, but one lead being ten(10) times the length of the other, while still having the same EMIcharacteristics.

Examples 2, 3, 4—Crosstalk Performance Example 2

FIG. 12 illustrates an example of an embodiment with two ground planes1200, 1202, both extending from the package substrate 1204 to the die1206 to permit connection at both lead ends.

Example 3

FIG. 13 illustrates an example embodiment with two ground planesrespectively forming an RF ground shield 1300 and a DC power groundshield 1302.

Example 4

In another embodiment, multiple impedance interconnects can be achievedthrough a variant of the above process. A substrate supporting a die iswire-bonded with 0.7 mil wire as appropriate for interconnect of allpackage and device pads. The resultant package assembly is subjected to1.31 microns of coating with Parylene™ C dielectric. A process to openvias to ground connections for power on the package and correspondingpower ground connections on the device is performed. A first selectivemetallization process is performed that creates metal only in areasassociated with the power interconnects and their associated grounds.This selective metallization is accomplished through physical masking,lithography, or other selective process. Thus, complete 5 ohm coaxialinterconnects have been formed. At this juncture, a second coating ofdielectric is deposited to achieve a total dielectric thickness of 26.34microns. A second via process is performed on all grounds needed forsignal lines. This step may also include connections to power supplyground if so desired. A second metallization is performed to create theground shield for the 50 ohm lines. Thus, a combination of 5 ohm and 50ohm interconnects is achieved, with the option of separate decoupledground planes for power and signal lines.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

In particular, the present invention is directed to: a stacked diepackage with superior EMI performance, comprising a first and a seconddie, with each die respectively having a plurality of connection pads, adie substrate supporting a plurality of connection elements, a firstlead extending from a first die to one of the plurality of connectionelements on the die substrate, the first lead having a first metal corewith a first core diameter, a dielectric layer surrounding the firstmetal core having a first dielectric thickness, and an outer metal layerattached to ground, and a second lead extending from a second die to oneof the plurality of connection elements on the die substrate, the secondlead having a second metal core with a second core diameter, and adielectric layer surrounding the second metal core having a seconddielectric thickness, and an outer metal layer attached to ground, toreduce susceptibility to EMI and crosstalk between first and secondleads.

The above die package, wherein the first lead crosses over the secondlead, or is above the second lead.

The die substrate can have filled vias to allow formation of BGApackage, and/or a leadframe to form a leadframe package.

The invention includes die to die connections as well as die tosubstrate connections.

Further, the present invention is directed to a BGA package withsuperior EMI performance, comprising a die having a plurality ofconnection pads, a die substrate supporting a plurality of connectionelements, a plurality of leads, each having a metal core, a dielectriclayer surrounding the metal core, and an outer metal layer connected toground, with crosstalk noise reduced greater than 5 dB as compared to aleads without a dielectric layer surrounding the metal core and an outermetal layer.

Further, the present invention includes a differential pair with reducedcrosstalk and crossover, long loop leads out of plane with reducedcrosstalk.

Further the present invention includes a die package, comprising a diehaving a plurality of connection pads, a die substrate supporting aplurality of connection elements, a first lead extending from a firstdie to one of the plurality of connection elements on the die substrate,the first lead having a first metal core with a first core diameter, adielectric layer surrounding the first metal core having a firstdielectric thickness, and an outer metal layer, a first ground planeattached to the outer metal layer of the first lead, a second leadextending from a second die to one of the plurality of connectionelements on the die substrate, the second lead having a second metalcore with a second core diameter, and a dielectric layer surrounding thesecond metal core having a second dielectric thickness, and a secondground plane attached to the outer metal layer of the second lead.

In the above die package, the second ground plane may overlay the firstground plane, with a intervening dielectric layer maintaining electricalisolation between the first and second ground planes.

The die package may be built in the form of a BGA package and/or aleadframe package.

Thus, having described the invention, what is claimed is:
 1. A diepackage comprising: a die having a plurality of connection pads; a diesubstrate supporting a plurality of connection elements; a first leadhaving a first metal core with a first metal core diameter, a firstdielectric layer surrounding said first metal core having a firstdielectric thickness, and a first outer metal layer surrounding saidfirst dielectric layer, said first outer metal layer attached to a firstground plane; and a second lead having a second metal core with a secondmetal core diameter, a second dielectric layer surrounding said secondmetal core having a second dielectric thickness, and a second outermetal layer surrounding said second dielectric layer, said second outermetal layer attached to a second ground plane; such that susceptibilityto EMI and crosstalk between the first and second leads are reduced,wherein the first ground plane is separate and distinct from the secondground plane.
 2. The die package of claim 1, wherein the first leadextends from a first die to one of the plurality of connection elementson the die substrate, and the second lead extends from a second die toone of the plurality of connection elements on the die substrate, thefirst ground plane attached to said first outer metal layer and thesecond ground plane attached to said second outer metal layer.
 3. Thedie package of claim 1, wherein the first metal core diameter differsfrom the second metal core diameter, or alternatively, wherein the firstmetal core diameter is the same as the second metal core diameter. 4.The die package of claim 1 wherein the die package includes a first anda second die, each of said dies having a plurality of connection pads,the first lead extending from said first die to one of said plurality ofconnection elements on said die substrate or to one of said plurality ofconnection pads of said second die, and the second lead extending fromsaid second die to one of said plurality of connection elements on saiddie substrate or to one of said plurality of connection pads of saidfirst die.
 5. The die package of claim 1 wherein, the first dielectriclayer thickness differs from the second dielectric layer thickness, oralternatively, wherein the first dielectric layer thickness is the sameas the second dielectric layer thickness.
 6. The die package of claim 1,wherein the die package is a stacked die package.
 7. The die package ofclaim 1, wherein said die substrate includes filled via to allowformation of a BGA package.
 8. The die package of claim 1, wherein thedie substrate includes a leadframe to form a leadframe package.
 9. Thedie package of claim 1, wherein the first lead crosses over the secondlead and/or is above the second lead.
 10. The die package of claim 1,wherein the first lead has a first length and a first impedance and thesecond lead has a second length and a second impedance, wherein saidfirst length is different from said second length and/or said firstimpedance is different from said second impedance.
 11. The die packageof claim 1, wherein said first metal core and/or said second metal coreis sequentially coated with a dielectric layer and a conductive metallayer.
 12. The die package of claim 1, wherein the first and secondleads provide electrical communication for die-to-die connection and/ordie-to-substrate connection.
 13. The die package of claim 1, wherein ofthe first and second leads include at least one differential pair. 14.The die package of claim 1 wherein the first and second leads includecrossover, long loop leads out of plane with reduced crosstalk.
 15. Adie package comprising: a die having a plurality of connection pads; adie substrate supporting a plurality of connection elements; a firstlead having a first metal core with a first metal core diameter, a firstdielectric layer surrounding said first metal core having a firstdielectric thickness, and a first outer metal layer surrounding saidfirst dielectric layer, said first outer metal layer attached to a firstground plane; and a second lead having a second metal core with a secondmetal core diameter, a second dielectric layer surrounding said secondmetal core having a second dielectric thickness, and a second outermetal layer surrounding said second dielectric layer, said second outermetal layer attached to a second ground plane; such that susceptibilityto EMI and crosstalk between the first and second leads are reduced;wherein the first ground plane is separate and distinct from the secondground plane; wherein the first lead extends from a first die to one ofthe plurality of connection elements on the die substrate, and thesecond lead extends from a second die to one of the plurality ofconnection elements on the die substrate, the first ground planeattached to said first outer metal layer and the second ground planeattached to said second outer metal layer; and wherein the second groundplane overlays the first ground plane with an intervening layermaintaining electrical isolation between the first and second groundplane.
 16. A BGA package with superior EMI performance including a diepackage comprising: a die having a plurality of connection pads; a diesubstrate supporting a plurality of connection elements; a first leadhaving a first metal core with a first metal core diameter, a firstdielectric layer surrounding said first metal core having a firstdielectric thickness, and a first outer metal layer surrounding saidfirst dielectric layer, said first outer metal layer attached to a firstground plane; and a second lead having a second metal core with a secondmetal core diameter, a second dielectric layer surrounding said secondmetal core having a second dielectric thickness, and a second outermetal layer surrounding said second dielectric layer, said second outermetal layer attached to a second ground plane; such that susceptibilityto EMI and crosstalk between the first and second leads are reducedwherein said crosstalk noise is reduced at least 5 dB as compared toleads without a dielectric layer surrounding the metal core and havingan outer metal layer, wherein the first ground plane is separate anddistinct from the second ground plane.
 17. A die package comprising: adie having a plurality of connection pads; a die substrate supporting aplurality of connection elements; a first lead having a first metal corewith a first metal core diameter, a first dielectric layer surroundingsaid first metal core having a first dielectric thickness, and a firstouter metal layer surrounding said first dielectric layer, said firstouter metal layer attached to a first ground plane; and a second leadhaving a second metal core with a second metal core diameter, a seconddielectric layer surrounding said second metal core having a seconddielectric thickness, and a second outer metal layer surrounding saidsecond dielectric layer, said second outer metal layer attached to asecond ground plane; such that susceptibility to EMI and crosstalkbetween the first and second leads are reduced, and wherein the firstground plane and the second ground plane are electrically distinct, butphysically overlap.